Restore beta4 for a devel release.
Merge pull request #1251 from sinzui/inc-1.21-beta4-again

Restore beta4 for a devel release.

The 1.21.0 version change branch was merged. I didn't intend it to be merged until stakeholders agreed they were ready for 1.21.0 in production.

(Review request: http://reviews.vapour.ws/r/562/)